Maintenance of engine lubricant quality and level is essential to the proper operation and long service life of an internal combustion engine. In general, lubricant level may vary during the operation of an engine due to lubricant leakage past various seals and some consumption of the lubricant which naturally occurs in the combustion cylinders. A responsibility of the engine operator is to periodically check the lubricant level and, if needed, add an appropriate amount of fresh lubricant to maintain the lubricant at a desired level. As used herein, the term "fresh lubricant" includes a base lubricant containing desired quantities and types of fresh lubricant additives.
In general, the quality of the lubricant in an engine degrades with engine use. Lubricant degradation occurs due to depletion of lubricant additives that perform specific functions such as control viscosity, reduce wear, increase lubricity, minimize deposits, prevent oxidation, and other desirable features. Lubricant degradation can also occur by the ingestion of foreign materials into the lubricant such as dirt from the surrounding environment, wear materials from the engines that occur as part of the natural operating process, and blow-by from the combustion process. Lubricant degradation can also occur due to a break-down of the base stock of the lubricant. In the extreme case fuel and/or water contamination of the lubricant can cause lubricant degradation.
Two ways of improving the quality of the engine lubricant is to periodically remove some or all of the engine lubricant and replace it with fresh lubricant. Also, in most cases filters are used to remove foreign materials above a certain size from the engine lubricant.
Various systems have been proposed for periodically removing a given quantity of lubricant from the engine and either storing the lubricant until it can properly be disposed of, or in the case of a diesel engine, optionally periodically injecting the lubricant into the fuel tank where the lubricant is mixed with the fuel and then burned in the engine along with the fuel. Also, it is generally known to provide such systems with automatic lubricant level sensing devices which maintain the proper level of lubricant in the engine.
In some systems, a given quantity of the engine lubricant is removed at preset time intervals based on engine usage factors. In others, small increments of engine lubricant are periodically removed and substantially simultaneously replaced with correspondingly small increments of fresh lubricant. In still others, a given amount of engine lubricant is periodically removed based on sensors that measure different operating variables of the engine such as the level, temperature and/or pressure of the lubricant within the engine, the number of engine starts or crank shaft revolutions, the length of time the engine has been in motion and at rest, engine temperature, fuel consumption, etc.
However, there is still a need for a system that more effectively determines the condition and thus the quality of the engine lubricant, and when the quality of the engine lubricant degrades a predetermined amount, periodically removes a portion of the engine lubricant and replaces it with fresh lubricant to maintain the quality of the engine lubricant above a predetermined minimum high level.